This invention relates to antennas and devices incorporating antennas. In particular, this invention relates to low cost miniature antennas for lightweight products that are very reproducible in high volumes and whose electrical characteristics are very repeatable.
Manufacturers of portable wireless devices such as handsets, personal digital assistants (PDA's) and laptops are constantly under extreme size and cost pressures. All of these wireless devices typically pack a substantial amount of circuitry in a very small package, which requires one or more antenna to communicate. The circuitry may include a logic circuit board and an RF circuit board. The printed circuit board can be considered a radio frequency (RF) ground to the antenna, which is ideally contained in the case with the circuitry. Thus, the ideal antenna would be one that can be placed extremely close to such a ground plane and still operate efficiently without adverse effects such as frequency detuning, reduced bandwidth, or compromised efficiency.
It is desirable to incorporate the antenna within the package or case for reasons of esthetics, durability and size. However, existing antennas for similar frequencies of operation used to decrease the size of the device still require a relatively large amount of space and weight. Furthermore, and most importantly, these existing antennas cost considerably more to manufacture than standard antennas. Various ways exist in which to design and manufacture low cost antennas for portable devices. The most common are external antennas, but these are quickly falling out of favor due to poor aesthetics and a high rate of needed repair and replacement.
Further, the Federal Communication Commission (FCC) mandates internal antennas for some applications in some standards, such as the IEEE 2.4 GHz Standard 802.11a, published by the Institute of Electrical and Electronic Engineers. Internal antennas are commonly manufactured using bent and shaped metal, making contact to the main product printed circuit board (PCB) with spring contact. Others types of internal antennas are miniaturized using high dielectrics or coils or both, and then simply surface mounted to the PCB. Disadvantages of these types of internal antennas include both that the manufacturing cost is much higher and the bandwidth covered by the antennas is much less, i.e. the performance suffers greatly. One example of this type of antenna is a meander line antenna manufactured by SkyCross, which employs multiple layers of metal internal to a solid multilayer PCB.
A variety of other antennas having small profiles have also been developed. These include Planar Inverted-F Antennas (PIFAs), types of shorted patches, meander line antennas and various derivatives. To date, however, none of the above antennas satisfy the present design goals, which specify efficient, compact, low profile antennas whose height is at most λ/60 above a ground plane. For example, there is a particular need for a 2.4 GHz antenna whose maximum height is at most 2.2 mm above a ground plane, and is thus well suited to devices requiring optimum performance in a compact volume, and operated according to the Bluetooth Standard.
Thus, there is a continuing need for simpler, lighter, and lower total cost internal antennas and devices using internal antennas. For example, to decrease the total cost of these antennas and devices, the cost of material or assembly labor should be reduced and/or yield increased during fabrication.
Another matter of importance to antenna electrical performance is the need to integrate the antenna into a package or onto a printed circuit board (PCB) of a radio communication system where the antenna and other surface mounted components can occupy the same, or a portion of the same, real estate. Furthermore, there is a need to extend the function of existing passive antennas to make them tunable or reconfigurable with the addition of switches or variable capacitors.